This invention relates to processes for chemically etching solid surfaces, particularly chemical etching processes involving the application of intense light, e.g. a laser. In addition, the process of the invention is especially related to chemical etching techniques for etching ionic substances having relatively low solubility or low chemical reactivity, such as used in integrated optical and acoustical devices.
Etching techniques generally involve bringing the surface of a substrate into contact with an etchant or bombarding the surface of a substrate with ions. In these processes the treated portion of the substrate surface is removed, i.e., etched, by for example diffusion or dissolution within a solvent. Some processes for etching surfaces involve a step wherein the substrate is exposed to high-intensity light. In these procesess, the high-intensity light is typically used either to generate a reactive species which will then act as an etchant or to directly etch the surface of vaporizing a reaction product formed during the process.
U.S. Pat. Nos. 3,489,564 and 3,520,685 disclose etching processes wherein a photo-decomposable fluorine compound, in contact with a silicon dioxide surface, is exposed to "activating radiation" energy to form a chemically reactive fluoro-species capable of etching the silicon dioxide surface. In U.S. Pat. No. 3,489,564 the photodecomposable fluorine compound is contained within an etching liquid and the silicon dioxide substrate is placed in contact with the liquid. Etching is performed by exposing the substrate/liquid etchant interface to a pattern of activating radiation. The surface of the substrate is etched at the interface by the resultant chemically reactive fluoro-species. In the process of U.S. Pat. No. 3,520,685 the photo-decomposable compound is contained within an organic polymeric solid film applied to the surface of the silicon dioxide substrate. The chemically reactive fluoro-species is produced by subjecting the interface between the substrate surface and the polymeric film to activating radiation through a metal mask in a humid atmosphere. The polymeric film is removed from the silicon dioxide subustrate by a solvent leaving behind a surface etched at the irradiated regions. Thus, in each of these processes the purpose of the activating radiation is to produce a chemically reactive species which is capable of etching the surface of a silicon dioxide substrate.
Another process wherein radiation is employed to produce a chemically reactive etching compound is disclosed in U.S. Pat. No. 4,536,252. In this process, a mixture of nitrogen oxide catalyst compounds and a fluoro compound selected from NF.sub.3 and N.sub.2 F.sub.4 by a continuous wave CO.sub.2 laser to produce nitrosyl fluoride, FNO. The chemically reactive species, FNO, is brought into contact with a silicon substrate, reacting with the silicon to produce SiF.sub.4 and nitrogen oxide thereby etching the substrate surface. FNO can either be produced directly within the etching chamber or optionally it can be produced in a side chamber and the resultant product gas then delivered to the etching chamber. The silicon substrate is exposed to the nitrosyl fluoride through a mask.
U.S. Pat. No. 4,478,677 also discloses a process wherein a laser is used to generate an active species for etching the surface of silicon dioxide or glass. In this process, a halogen gas is flowed into a chamber containing the substrate to be etched whereby the halogen gas wets the substrate surface. The wetted surface is then exposed through the gas to a pattern of light generated from a laser. The surface on which the light impinges is excited and the gas wetting the surface forms an active species capable of etching the surface in conformity with the pattern of light.
U.S. Pat. No. 4,490,211 discloses a method for etching metals on the surface of the substrate by using an excimer laser to vaporize the products formed by a spontaneous reaction between the metal and the halogen gas. In this process, the intended purpose of thin laser is not to form a chemically reactive etching species. Instead, the laser is used to directly etch the surface of the metal film by removing the product from the reaction between the metal surface and the halogen gas.
In each of these etching processes, activating radiation or high-intensity lasers are used to produce a chemically reactive species or to vaporize reaction products. Furthermore, these processes are directed to the etching of certain specific substrates such as glass, Si, SiO.sub.2 or metal films.